The present invention relates to an abradable coating and more particularly to applying such abradable coating in a turbomachine.
In turbomachines, such as centrifugal compressors, axial compressors, and turbines, rotating blades attach or are integral with a rotor assembly. A shroud surrounding the rotating blades acts in conjunction with the rotating blades to keep a pressurized fluid flowing in a particular direction. Pressurized fluid tends towards migrating to areas of lower pressure. In many instances, pressurized fluid will pass to a lower pressure region by escaping between the blades and the shroud.
To reduce migration of pressurized fluid and therefore improve efficiency of the turbomachine, clearances between the blades and housing must be reduced to a minimum. In U.S. Pat. No. 6,039,535 issued to Kobayashi et al Mar. 21, 2000, a seal is placed on the shroud of a centrifugal compressor. The seal includes a portion covered with an abradable material. A fin extends from the rotor to close proximity with the abradable material. The fins are designed to create a groove in the abradable coating as the turbomachinery reaches some operating condition. By creating the groove, the fin and seal form very close tolerances. However, the abradable material eventually wears away from the rotor through peeling.
Similarly, in an axial flow rotating machine the fins of the seal are placed on tips of the blades. An abradable seal is attached to the shroud. In U.S. Pat. No. 4,867,639 issued on Sep. 19, 1989 to Strangman, the abradable seal is a soft ceramic material in a honeycomb substrate. However, ceramics may be costly and complex. While the cost and complexity may be needed at temperature upwards of 2300 F, lower cost and lower complexity abradable seals with good wear resistance are needed for lower temperature applications.
The present invention is directed at overcoming one or more of the problems as set forth above.
In one aspect of the present invention a turbomachine has improved efficiency. The turbomachine has a rotor with a plurality of blades. A shroud is spaced radially outward from the rotor. A sealing portion is between the shroud and the rotor. an abradable coating covers at least a portion of the sealing portion. The abradable coating includes a solid lubricant and a metal alloy having a quasicrystalline phase.
In another embodiment of the present invention an abradable coating comprise by weight about: 2-16 percent copper; 5-20 percent solid lubricant; 3-7 percent silicon; 1-9 percent chromium; 1-12 percent iron; 3-7 percent polyester; and balance composed of aluminum and traces of other elements wherein at least a portion of aluminum being in a quasicrystalline phase.